The challenges to forensic body fluid analysis have placed limitations on the type of information that investigators can acquire and how that information can be collected. In recent years, Raman spectroscopy has proven itself useful for characterizing body fluids. In 2008, a large-scale investigation was undertaken to explore the use of Raman spectroscopy as a means of identifying body fluids. This work resulted in multidimensional Raman spectroscopic signatures for the five main body fluids: semen, peripheral blood, saliva, vaginal fluid, and sweat. These studies were incredibly successful and created the foundation for years of continued research. Accordingly, the studies included in this thesis have been specifically chosen to frame the previous research projects. They include a suite of projects aimed to advance and validate the developed method.
First, a statistical model was developed to automatically identify and differentiate body fluids based on their Raman spectra. The multidimensional spectroscopic signatures mentioned above are very effective at identification, but they are body fluid-specific. In other words, they individually evaluate whether or not an unknown spectrum is from a particular body fluid, such as blood. Additionally, each signature was built on spectra from a limited number of donors. To improve on this capability, a single classification model was built on the Raman spectra from 60 donors (12 for each body fluid). This model was externally validated with an additional 15 donors in order to objectively assess the model’s performance. All of the external validation donors were correctly identified, illustrating how accurate and robust the model is.
Second, the limit of detection (LOD) for the classification model was explored as a form of validation. It is vitally important that a method’s limits be established before deploying it into use. The LOD of peripheral blood was investigated. Peripheral blood is unique from other body fluids because its Raman spectrum has been attributed almost entirely to one molecule- hemoglobin. Because hemoglobin is only found in red blood cells (RBCs), the Raman spectrum of peripheral blood essentially results purely from RBCs. Given this, we chose to start with a single RBC, and then increase the volume until identification was successful. We found that we were able to conclusively and confidently identify peripheral blood using a single red blood cell. This limit is 5000X smaller than the amount of blood required for DNA analysis, demonstrating the sensitivity of the developed method.
Finally, the method was further advanced by incorporating donor characterization into the process. Besides identifying body fluids, the method can now extract “phenotypic” information about the donor. Raman spectroscopy and multivariate data analysis were used to determine the biological sex of saliva donors, and the race of semen donors. These studies will help forensic investigators extract incredibly useful information about a potential suspect or victim, and can be performed directly at a crime scene for instant results.
Altogether, these studies combine to strengthen the method previously developed by our research group. More importantly, they help to bridge the gap between research and application. Creating a universal method to differentiate and identify body fluids, investigating the method’s LOD, and developing additional techniques to characterize body fluids represents a significant contribution to the field of forensic chemistry. The universal method created within this thesis will be adapted to perform on-site analysis of physical evidence at crime scenes. The methods’ incredible sensitivity has been demonstrated by determining that it can identify peripheral blood based on a single RBC. Finally, by developing models to characterize body fluid donors, investigators will be able to extract useful information about individuals that may have been present at a crime scene. Additional studies are already being conducted to make further improvements, and our method is poised to make a significant contribution to the field of crime scene investigation.
|Advisor:||Lednev, Igor K.|
|Commitee:||Gettig, Russell, Halamek, Jan, Pande, Jayanti, Shekhtman, Alexander|
|School:||State University of New York at Albany|
|School Location:||United States -- New York|
|Source:||DAI-B 78/11(E), Dissertation Abstracts International|
|Subjects:||Chemistry, Analytical chemistry, Biochemistry|
|Keywords:||Body fluids, Chemometrics, Forensics, Multivariate data analysis, Spectroscopy|
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